I built a bar on the weekend and am going to need to make/buy a custom
countertop for behind it.

It is L shaped and the sink side will be only 18 inches wide (to the
wall). I heard a total custom top would be pretty expensive.

I'm thinking of gluing some arborite to a custom wood base.

Do you have a link to a "how to" thread for this?

I need to know how thick the base ply should be and some cutting,
gluing, trimming instructions.

Thanks in advance.